The use of radiation to treat medical conditions comprises a known area of prior art endeavor. For example, radiation therapy comprises an important component of many treatment plans for reducing or eliminating unwanted tumors. Unfortunately, applied radiation does not discriminate between unwanted structures and adjacent tissues, organs, or the like that are desired or even critical to continued survival of the patient. As a result, radiation is ordinarily applied in a carefully administered manner to at least attempt to restrict the radiation to a given target volume.
Many radiation-delivery treatment plans provide for exposing a treatment target (such as a tumor) to radiation from a plurality of different directions during a single treatment session. So-called arc therapy is one illustrative example in these regards. In such a case a gantry-based apparatus typically serves to move a radiation source along an arc about the patient during the treatment session.
In some cases administering the radiation also includes tracking motion as pertains to the patient. This can comprise, for example, real-time tracking of an absolute and/or relative position of the treatment target, critical organs to be protected from the radiation, a man-made marker, and so forth. Such tracking can also comprise, for example, tracking rhythmic movement such as the patient's breathing. In these cases the radiation-delivery treatment plan can facilitate automatically compensating for motion by automatically and responsively adjusting one or more radiation-delivery parameters. As one simple example, this can comprise shutting off the radiation source when the tracked movement reveals that the treatment target has moved beyond an expected target region.
Radiation-delivery treatment plans that compensate for motion typically employ a limit as pertains to a given motion compensation-based adjustment. Such limits, for example, can reflect physical limitations of the treatment apparatus and can serve to avoid having the treatment apparatus attempt a compensation adjustment that is physically difficult or even impossible. In another example, the limits reflect safety values that prevent delivering too much radiation to critical organs. Unfortunately, however, numerous variables are in play during a treatment session and such limits often represent a compromise between permitting dynamic flexibility on the one hand and achieving treatment goals on the other hand. This compromised result, in turn, may yield a less efficacious therapy than might in fact be possible.
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.